Klein Tools MM420 Digital Multimeter, Auto-Ranging TRMS Multimeter, 600V AC/DC Voltage, 10A AC/DC Current, 50 MOhms Resistance

Why it's worth it

The Klein MM420 is a true RMS meter with a drop rating and LEDs that tell you when your leads are in the wrong jacks. It skips the engine-management extras, so it's the pick if you chase wiring and charging faults more than driveability complaints.

True RMS is the reason to choose this one. Cars switch things on and off constantly now, and the resulting waveforms aren't smooth sine waves. Average-responding meters guess at them and guess badly. The MM420 calculates the actual effective value regardless of waveform shape, so what you read on a PWM fan circuit or a modern alternator is what's really there.

The Lead-Alert LEDs prevent the mistake that kills meters. LEDs on the face light up to confirm your probes are in the right jacks. Leave a lead in the current input, switch to volts, touch a live circuit, and you've just made a dead short — it's the single most common way people destroy a multimeter. Klein made that error visible before you take the reading rather than after.

From our review of 8 automotive multimeters, by Ben Carter, Tech Editor

What we like

• +True RMS is the reason to choose this one
• +The Lead-Alert LEDs prevent the mistake that kills meters
• +It's rated to survive a fall from a stepladder
• +The measurement coverage is broad

What to know

• –There's no RPM clamp and no dwell
• –The current ceiling and the temperature probe both come with caveats